An oil catch can removes all the oil vapors and sludge that normally gets put back into the engine thru the valve cover breather hoses into the manifold just past the throttle body.
The 2 hoses ( 1 from each side ) from the valve covers go to the catch can, another hose goes from the catch can back to the manifold.
If you look at the attached picture, the catch can is the thing right in front of the brake master cylinder.
Mine is from Needswings at $127.95 (
NeedsWings Crossfire Oil Catch Can Kit ), but others have used generic ones from Ebay ......